The invention relates generally to a device for moving a spray coating apparatus with respect to a workpiece and, in particular, to such a reciprocating device in which the speed and distance of movement can be adjusted.
In the prior art, a plurality of workpieces to be coated are typically moved by a conveyor past one or more spray guns for spraying the coating. The spray guns are either stationary or are mounted to swing up and down or to and fro, the deflection from the central point of the swinging movement usually being adjustable.
The best movement for the gun is usually dictated by the shape of the workpiece. A spraying apparatus for automatically coating workpieces having a complicated shape is disclosed in U.S. Pat. No. 3,606,162. In this patent, a spray gun is mounted on a carrier head for pivoting movement in a vertical plane. The carrier head is mounted on a lifting stand for vertical up and down movement and the lifting stand is placed on a carriage means for movement in a horizontal plane in two directions at right angles to each other. The movements of the spray gun, lifting stand, and carriage means are effected by motors controlled by programmed control devices adapted to be set to produce a sequence of operating steps of the spray gun, lifting stand, and carriage means. The motors are direct current motors which are controlled as to direction of rotation, speed, and running time.
U.S. Pat. No. 4,125,035 discloses a control mechanism for spray guns which includes a rectangular frame having crossing supporting rods extending between opposite frame members. A mounting member is slidably mounted on crossing portions of the rods and carries a spray gun which can be moved toward and away from the mounting member in a direction perpendicular to the plane of the frame. The spray guy can also be pivotally moved on a first axis which is parallel to the plane of the frame and pivotally moved on a second axis which can also be parallel to the frame and perpendicular to the first axis. The spray gun can also be pivotally moved about an axis which is perpendicular to one of the aforesaid axes.
In another form of reciprocating device, two vertically spaced apart sprocket wheels are joined by an endless chain and a pin fixed to the chain moves in a horizontally disposed slot in a support for a spraying device such that reciprocation of the reciprocating member is achieved by the movements of the chain. This device has a disadvantage since the reciprocating member must reciprocate over the full distance between the two sprocket wheels regardless of the size of the object to be painted.
U.S. Pat. No. 4,378,705 discloses a reciprocating device in which a reciprocating member alternately and selectively engages with either the upwardly moving side or the downwardly moving side of an endless member such as a chain or belt which is running in one direction. Thus, the range of reciprocating movement can be determined by the timing of the mechanism for alternately engaging the two sides of the chain.
U.S. Pat. No. 4,404,870 discloses a reciprocator for a paint gun which has a plurality of fixed pulleys and a plurality of moveable pulleys, the moveable pulleys being reciprocated upwardly and downwardly. A slider on which the paint gun is mounted is attached to one end of a wire which is threaded through the pulleys and fixed at the other end for moving the paint gun as the moveable pulleys are reciprocated.
In another form of prior art spraying device, a pair of spaced apart, generally vertically extending bars are pivotally attached to opposite ends of a pair of generally parallel spaced apart horizontally extending bars. One of the vertical bars is fixed with respect to a work piece to be coated and the other vertically extending bar has one or more spray painting devices attached to it. The lower one of the generally horizontally extending bars is pivotally attached to a crank arm between its ends which in turn is driven by a motor, thereby reciprocating the two horizontal bars and the one free vertical bar in an arcuate path. The excursion of the reciprocating motion can be adjusted by moving the attachment point of the crank arm to the lower horizontal bar. One disadvantage of this type of device is that the spray painting devices move in a arc rather than in a straight vertical path parallel to the work piece.